Problem: $-7de + e + 9f + 3 = 8e - 3f - 9$ Solve for $d$.
Answer: Combine constant terms on the right. $-7de + e + 9f + {3} = 8e - 3f - {9}$ $-7de + e + 9f = 8e - 3f - {12}$ Combine $f$ terms on the right. $-7de + e + {9f} = 8e - {3f} - 12$ $-7de + e = 8e - {12f} - 12$ Combine $e$ terms on the right. $-7de + {e} = {8e} - 12f - 12$ $-7de = {7e} - 12f - 12$ Isolate $d$ $-{7}d{e} = 7e - 12f - 12$ $d = \dfrac{ 7e - 12f - 12 }{ -{7e} }$ Swap the signs so the denominator isn't negative. $d = \dfrac{ -{7}e + {12}f + {12} }{ {7e} }$